The precise cardiovascular effect of dietary fats and supplements has been the subject of heated controversy. Although there is no strong supporting evidence from clinical trials, current guidelines tend to discourage or minimize the role of saturated fats and trans fats and to encourage the intake of omega-3 polyunsaturated fatty acids. Two new studies published today help clarify some of the issues. Both studies demonstrate the shaky underpinnings of the guidelines but are unlikely to provide firm support for a new perspective on these issues.

In an exceedingly strange turn of events, data from a clinical trial dating from the 1960s, long thought to be lost, has now been resurrected and may contribute important new information to the very contemporary controversy over recommendations about dietary fat composition.

The American Heart Association has long urged people to increase their consumption of polyunsaturated fatty acids (PUFAs), including omega 6 PUFAs, and reduce their consumption of saturated fatty acids. The recommendations are based on the simple observation that PUFAs lower total and LDL cholesterol while SFAs have the opposite effect. However, the cardiovascular effects of substituting PUFAs for SFAs have never been tested in randomized, well-controlled clinical trials, and a growing proportion of experts now suspect that simple changes in total cholesterol and LDL cholesterol may not tell the whole story.

One trial that actually tested the hypothesis was the Sydney Diet Heart Study, which ran from 1966 through 1973. In the trial, 458 men with coronary disease were randomized to a diet rich in linoleic acid (the predominant omega 6 PUFA in most diets) or their usual diet. Although total cholesterol was reduced by 13% in the treatment group during the study, all-cause mortality was higher in the linoleic acid group than in the control group. However, in the original publications, and consistent with the practice at the time, deaths from cardiovascular (CVD) and coronary heart disease (CHD) deaths were not published.

Now, in a new paper published in BMJ, Christopher Ramsden and colleagues report that they were able to recover and analyze data from the original magnetic tape of the Sydney Diet Heart Study. The new mortality findings are consistent: